Our new boards for Dynaco Mk4 are identical circuitwise (cascode input with long-tail pair phase inverter) to our Mk3/Mk2 boards, but resized to fit the Mk4. Each amplifier requires one 12AU7 plus one each of either 12AU7, 12BH7, 6CG7/6FQ7 or 6N1-P. Tubes are not included with kits.
"Blank Board" means just that, you supply the parts.
"With Parts" means all board parts, you solder on board
For more information please see our Dynaco Page
Here is the Driver Board Instructions
Note that Sprague 715P/716P Orange Drop capacitors will not fit this board.
Here are the instructions for changing thr Mk4 to triode operation:
Find the green (not green/white) wire (one from the output transformer) hooked to pin 4 on an EL34, there is also a wire leading from that pin to pad 4 on the circuit board.
Disconnect the green wire from pin 4 and run directly to pad 4 of the circuit board.
Remove the wire that previously ran from pad 4 to the EL34/6550 sockets.
Disconnect the screen tap lead (green/white) from pin 4 of the other output tube, then insulate the end of the wire so that the bare leads are not exposed.
Install a 100 ohm (1/2 watt minimum) resistor between pin 3 and pin 4 of each of the output tube sockets.
Reinstall the output tubes, and recheck bias (BIASET on front panel).
|Mk4 Upgrade Driver Board Blank Blank upgrade board for Dynaco Mk4 amplifier.
Includes instructions but no parts.Each amplifier requires one board.|
|Mk4 Upgrade Driver Board with PartsUpgrade board with parts for Dynaco Mk4 amplifier.
Includes instructions and all parts required for completion except for the tubes.Each amplifier requires one board.|
|Dual Bias Kit for Dynaco Mk4 Amplifiers with Triode Electronics boardThis allows for biasing each EL34 tube
individually rather than as a pair, note that a hole
must be drilled for an additional bias control to use this.
Kit includes parts that are in the regular Bias Repair kit as well.This kit works only with our board. One kit required per amplifier|
|Bias Repair Set for Dynaco ST70 & Mk4.Replaces selenium bias rectifier with silicon diode,
also includes resistors & capacitors used in bias circuit
that are not on the printed circuit board. Parts Included: 10K 2W Resistors x 2pcs, .022uF 630V Capacitors x 2pcs, 100uF 100V Capacitors x 2pcs, & 1N4007 Diode. Not needed on ST70 if you install the SDS Labs Capacitor board|
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